sedimentary

Chert (Iron-stained)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Tan to white with orange-red iron oxide staining; Luster: Waxy to dull; Structure: Non-crystalline mass (microscopic crystals); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Tan to white with orange-red iron oxide staining
Luster: Waxy to dull

Identified March 26, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the precipitation of silica from groundwater or within deep-sea marine sediments. This specimen appears to be a nodule or fragment from a limestone host rock, likely Paleozoic to Mesozoic in age.

Uses & applications

Historically used for stone tools (arrowheads/scrapers) due to sharp edges; currently used for road ballast, crushed stone, and occasionally as lapidary rough for tumbling.

Geological facts

Chert is so hard it can scratch steel and glass. It was one of the first materials used by early humans to create fire because it produces sparks when struck against iron or steel.

Field identification & locations

Identify in the field by its hardness (cannot be scratched by a knife), waxy luster, and shell-like (conchoidal) curves where it is broken. Very common in limestone-rich regions like the Midwestern United States.

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